Compliant die attach tools, die attach systems, and methods of using the same

ABSTRACT

A die attach system is provided. The die attach system includes: a support structure for supporting a substrate; a die supply source including a plurality of die for attaching to the substrate; and a bond head for bonding a die from the die supply source to the substrate, the bond head including a bond tool having a contact portion for contacting the die during a transfer from the die supply source to the substrate, the bond head including a spring portion engaged with the bond tool such that the spring portion is configured to compress during pressing of the die against the substrate using the contact portion of the bond tool.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/727,395, filed Sep. 5, 2018, the content of which is incorporatedherein by reference.

FIELD

The invention relates to systems and methods for attaching a die tosubstrate, and more particularly, to improved compliant die attach toolsused in connection with attaching a die to a substrate without pickingthe die from a die supply source.

BACKGROUND

In connection with the placement of a die on a substrate (e.g.,semiconductor die attach operations), many conventional applicationsutilize a “pick and place” operation. In such operations, a die is“picked” from a semiconductor wafer or other die supply source, and thenthe die is moved to (and “placed” on) a target substrate. Suchoperations may also utilize one or more transfers between a “pick” tooland a “place” tool.

In other die attach operations, a die supply source (e.g., a waferincluding a plurality of die) may be positioned between a bond tool anda substrate. The bond tool may be used to press the die against thesubstrate while the die is still secured to a film/foil of the diesupply source. Thus, the die attach operation is performed without any“picking” and “placing” operation. However, such operations tend tosuffer from a number of deficiencies such as poor control of bond forcebetween the bond tool and the die during the bonding operation.

Thus, it would be desirable to provide improved die attach systems, andrelated methods, for overcoming one or more deficiencies of conventiondie attach systems.

SUMMARY

According to an exemplary embodiment of the invention, a die attachsystem is provided. The die attach system includes: a support structurefor supporting a substrate; a die supply source including a plurality ofdie for attaching to the substrate; and a bond head for bonding a diefrom the die supply source to the substrate, the bond head including abond tool having a contact portion for contacting the die during atransfer from the die supply source to the substrate, the bond headincluding a spring portion engaged with the bond tool such that thespring portion is configured to compress during pressing of the dieagainst the substrate using the contact portion of the bond tool.

According to another exemplary embodiment of the invention, a method ofattaching a die to a substrate is provided. The method includes thesteps of: providing a die supply source including a plurality of die forattaching to the substrate, the die supply source being positionedbetween a bond tool and a support structure supporting the substrate;and moving the bond tool, carried by a bond head, downward such that acontact portion of the bond tool contacts the die to transfer the diefrom the die supply source to the substrate. The bond head includes aspring portion engaged with the bond tool such that the spring portionis configured to compress during pressing of the die against thesubstrate using the contact portion of the bond tool.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity.

FIGS. 1A-1C are block diagram views illustrating elements of a dieattach system in accordance with an exemplary embodiment of the presentinvention; and

FIGS. 2A-2D are a series of side sectional views of a portion of a dieattach system in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

Certain die attach applications do not utilize a pick and placeoperation. For example, a die supply source (e.g., a wafer including aplurality of die, such as an LED wafer or other source of LED die) maybe positioned between a bond tool and a substrate. Die (e.g., an LEDdie) included in the die supply source may be attached to a film/foil orthe like.

According to certain exemplary aspects of the invention, after alignmentbetween the bond tool, the die to be attached, and a placement locationof the substrate—the bond tool presses the die against the placementlocation of the substrate. Adhesive on a lower surface of the die(and/or on the placement location of the substrate) is provided suchthat the die is now secured to the substrate. Such bond tools mayinclude a plurality of pins (e.g., actuatable pins, which may actuatedindependent of one another) for contacting the die in connection with atransfer from the die supply source to the substrate.

As used herein, the term “die” is intended to refer to any structureincluding (or configured to include at a later step) a semiconductorchip or die. Exemplary “die” elements include a bare semiconductor dieincluding a bare LED semiconductor die, a semiconductor die on asubstrate (e.g., a leadframe, a PCB, a carrier, a semiconductor chip, asemiconductor wafer, a BGA substrate, a semiconductor element, etc.), apackaged semiconductor device, a flip chip semiconductor device, a dieembedded in a substrate, amongst others.

According to certain exemplary embodiments of the present invention, ina die attachment system a bond head is used to attach a die to asubstrate. The bond head includes a holder (e.g., a shaft portion) and abond tool (e.g., a needle) coupled to the holder. The bond tool may besuspended in a housing of the bond head and can move in at least onedirection (e.g., along a vertical z-axis of the die attached system). Inthis way, the housing portion of the bond head is decoupled from thebond tool. The bond head includes a detection system (e.g., a sensor fordetecting an amount of compression of the spring portion during bondingof the die to the substrate) for detecting (e.g., measuring) movement ofthe bond tool relative to the bond tool housing. The die attach systemcontrols the movement of the bond tool on the basis of the signaldelivered by the detection system. In certain embodiments of theinvention, no such detection system or sensor is utilized. For example,control of the bond tool may be accomplished using other informationthat may be available. For example, motor current of the z-actuator(that drives the bond head along the z-axis, as part of a motionsystem—see element 124 in FIGS. 2A-2D) may be used to determine heightand/or to control motion of the bond tool.

Exemplary situations for use of the die attach system include: (i) thebond head may include a detection system to enable relative positionmeasurement between the bond tool housing and the bond tool; and (ii)the bond head may be used without such a detection system.

Exemplary purposes of various aspects of the invention include one ormore of the following: (i) reducing impact mass that the bond toolexerts on a die during die attach to a substrate; (ii) controlling theforce exerted by the bond tool on the die being attached; (iii)controlling the amount of compression of a spring portion of a bondhead; (iv) determining a point in time of collision of the die on thesubstrate during die attach; and (v) determining a collision height ofthe die on the substrate.

FIG. 1A illustrates die attach system 100. Die attach system 100includes a support structure 102 for supporting a substrate 104, a diesupply source 106 including a plurality of die 106 a configured to beattached to substrate 104, and a bond head 108 (which is configured tobe driven along a z-axis using motion system 124) including a bond tool120 for contacting die 106 a during a transfer of die 106 a from diesupply source 106 to substrate 104. Die attach system 100 also includesa bond head support 126 and a supply support 128. Bond head support 126and supply support 128 are each mounted on machine structure 130 suchthat bond head support 126 and supply support 128 are independentlymoveable relative to machine structure 130. Bond head support 126supports intermediate support structure 132 (which is moveable withrespect to bond head support 126), which supports moveable bond head108. Intermediate support structure 132 carries a camera 134 (and othervisions system components) for use in connection with alignment and/orinspection operations. Die supply source 106 is moveably mounted onsupply support 128. In the exemplary embodiment of the invention shownin FIG. 1A (and in FIG. 1B), during a die attach operation, die supplysource 106 is positioned between bond tool 120 and substrate 104supported by support structure 102. FIG. 1B is a cross-sectional sideview of elements of die attach system 100, with camera 134 and bond tool120 positioned over substrate 104. Two “bonded” die 106 a′ have beenbonded to substrate 104 at respective bonding locations and bond tool120 is shown engaging another die 106 a above a third respective bondinglocation on substrate 104. FIG. 1C illustrates a block diagram of anexample of bond tool 120. More specifically, bond tool 120 may includeat least one pin 120 b for contacting die 106 a in connection with atransfer from die supply source 106 to substrate 104. Further, as shownin FIG. 1C, bond tool 120 may include a plurality of pins 120 b forcontacting die 106 a in connection with a transfer from die supplysource 106 to substrate 104. Each of the plurality of pins 120 b may beseparably, or collectively, moveable (e.g., along a vertical axis) withrespect to the remainder of bond tool 120 to transfer die 106 a tosubstrate 104. Of course, bond tool 120 including one or more pins 120 b(as shown in FIG. 1C) is an example of bond tool 120. In otherembodiments of the invention, bond tool 120 may not include pins 120 b,but may transfer die 106 a without pins 120 b. Further still, FIGS.2A-2D illustrate bond tool 120 without pins 120 b, such that a singlestructure is driven along the z-axis. In embodiments of the inventionwhere bond tool 120 includes a plurality of pins 120 b, such pins mayinclude an additional actuator(s) for moving pins 120 b separately fromone another (or together) as desired to accomplish the die transfer.

FIGS. 2A-2D are a series of side sectional views, of a specificconfiguration of elements of die attach system 100. As provided above,die attach system 100 includes support structure 102 for supportingsubstrate 104, and die supply source 106 (e.g., wherein the die supplysource includes an LED wafer, and the plurality of die are a pluralityof LED die) including a plurality of die 106 a for attaching tosubstrate 104. For example, die supply source 106 includes a flexiblefilm 106 b, where the plurality of die 106 a are attached to flexiblefilm 106 b. Die attach system 100 includes bond head 108 for bonding die106 a from die supply source 106 to substrate 104. Bond head 108including a bond tool 120 (e.g., including a needle, a pin, a pluralityof pins that are separately moveable along a vertical axis, etc.)(wherein bond tool 120, such as the plurality of pins, contacts die 106a in connection with the transfer from die supply source 106 tosubstrate 104) having a contact portion 120 a for contacting die 106 aduring a transfer from die supply source 106 to substrate 104. Bond head108 includes a spring portion 118 engaged with bond tool 120 such thatspring portion 118 is configured to compress during pressing of die 106a against substrate 104 using contact portion 120 a of bond tool 120.Thus, bond tool 120 is spring loaded. In the example shown in FIGS.2A-2D, the engagement between spring portion 118 and bond tool 120 isvia a shaft portion 114 (e.g., a needle holder) included in bond head108. Bond tool 120 is secured to shaft portion 114 (either directly orindirectly). Shaft portion 114 is configured to move along a verticalaxis (e.g., a z-axis of die attach system 100).

More specifically, bond head 108 includes a z-actuator portion 110coupled to (either directly or indirectly) a bond tool housing 112. Bondhead 108 defines an interior aperture 108 a allowing for motion of shaftportion 114 along the aforementioned vertical axis. Spring portion 118is engaged with a portion of shaft portion 114. A plurality of linearguides 116 (e.g., play-free, frictionless, linear guides) are coupledbetween shaft portion 114 and bond tool housing 112. A stepped portion114 b of shaft 114 is configured to travel within a portion of interioraperture 108 a. Shaft portion 114 includes a pretensioned conicalportion 114 a configured to rest against an angled interior surface ofinterior aperture 108 a. More specifically, pretensioned conical portion114 a is under “tension” because of a force provided by spring portion118 which pushes against another stepped portion 114 c of shaft portion114.

Referring specifically to FIG. 2A, bond tool 120 is positioned above oneof the plurality of die 106 a (i.e., die supply source 106 is positionedbetween substrate 104 and bond tool 120). In FIG. 2A, bond tool 120(coupled to shaft 114, directly or indirectly) is in a lower positionwithin its range of motion with respect to bond tool housing 112. InFIG. 2B, bond head 108 has been moved downward such that contact portion120 a of bond tool 120 touches die 106 a of die supply source 106. Bondhead 108 continues to move downward such that film 106 b begins to move(i.e., flex) downward toward substrate 104. Spring portion 118 beginscompression during contact between the contact portion 120 a and die 106a prior to pressing of die 106 a against substrate 104 using contactportion 120 a of bond tool 120 (i.e., the compression in spring portion118 is shown in the difference between FIG. 2B and FIG. 2C).

FIG. 2C illustrates die 106 a being pressed against substrate 104 bybond tool 120 (e.g., with a force being equal to the displacement ofbond tool 120 times the spring constant of spring portion 118). That is,bond tool 120 (coupled to shaft 114, directly or indirectly) is now inan upper position within its range of motion with respect to bond toolhousing 112. The displacement of bond tool 120 is measured by adisplacement measuring device 122 (e.g., where the displacementmeasuring device may include a position sensor), which is included inz-actuator portion 110. A displacement signal (e.g., provided bydisplacement measuring device 122) is used by motion system 124 (formoving bond head 108) to stop the z-axis movement of bond head 108 at aposition corresponding to a predefined downward pressing force (i.e.,the position shown in FIG. 2C). It should be understood that such adisplacement signal may be used “real time” (in connection with apresent die attach operation, or such a displacement signal may be usedin connection with subsequent die attach operations.

After a bonding time (also referred to as a “dwell” time, i.e., the timeduring which bond tool 120 maintains the preset downward pressingforce), motion system 124 begins to raise bond head 108 upward as shownin FIG. 2D. Die 106 a is now bonded to substrate 104 (e.g., due aholding force by an adhesive included on substrate 104 and/or die 106 a)(where at least one of die 106 a, and a bonding location of substrate104, includes adhesive for securing die 106 a to the bonding locationafter the transfer from die supply source 106 to substrate 104). Thatis, as bond tool 120 is moved upward (carried by bond head 108), die 106a is released from film 106 b through a “jerk” movement of bond tool120. This jerk movement of bond tool 120 is caused by the upwardmovement of bond tool 120 as it returns to the lower position within itsrange of motion with respect to bond tool housing 112, due to the springforce.

Die attach system 100 is configured to control descent of bond tool 120(included in bond head 108) during the bonding of die 106 a to substrate104 based on feedback from displacement measuring device 122. Forexample, displacement measuring device 122 includes a position sensorfor detecting an amount of compression of spring portion 118 duringbonding of die 106 a to substrate 104.

Displacement measuring device 122 may vary within the scope of theinvention, and may operate in connection with motion system 124.Further, predetermined data may be used in connection with the operationof motion system 124. Such predetermined data may relate to (i) anamount of compression of spring portion 118 to provide a desirablebonding of die 106 a to substrate 104, where the amount of compressionis related to a z-axis position of at least one of (a) a portion of bondhead 108, and (b) a portion of bond tool 120; and/or (ii) an amount ofbond force to be applied to provide a desirable bonding of die 106 a tosubstrate 104, wherein the amount of bond force is related to a z-axisposition of at least one of (a) a portion of bond head 108, and (b) aportion of bond tool 120.

Exemplary benefits over conventional tools (and related die attachsystems) may include: (i) reducing forces exerted on a die during dieattach; (ii) optimizing output by minimizing move distances; (iii)enabling accurate height teaching in the system; and (iv) detectingirregular height variations which can cause process errors. Examples aredetection of obstructions on substrates, detection of missing dies onsource\substrate, and detection of system malfunction.

While the invention has been described and illustrated primarily withrespect to die attach operations where there is no “pick” operation, itis not limited thereto. The invention has broad applicability in thesemiconductor bonding industry including die attach machines (sometimesreferred to as die bonders) or other packaging machines (e.g., flip chipmachines/operations, advanced packaging operations, etc.).

Although the invention has been described and illustrated with respectto the exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, without partingfrom the spirit and scope of the present invention. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the invention.

What is claimed:
 1. A die attach system comprising: a support structurefor supporting a substrate; a die supply source including a plurality ofdie for attaching to the substrate; and a bond head for bonding a diefrom the die supply source to the substrate, the bond head including abond tool having a contact portion for contacting the die during atransfer from the die supply source to the substrate, the bond headincluding a spring portion engaged with the bond tool such that thespring portion is configured to compress during pressing of the dieagainst the substrate using the contact portion of the bond tool.
 2. Thedie attach system of claim 1 wherein the spring portion beginscompression during contact between the contact portion and the die priorto pressing of the die against the substrate using the contact portionof the bond tool.
 3. The die attach system of claim 1 further comprisinga sensor for detecting an amount of compression of the spring portionduring bonding of the die to the substrate.
 4. The die attach system ofclaim 3 wherein the die attach system is configured to control descentof the bond tool during the bonding of the die to the substrate based onfeedback from the sensor.
 5. The die attach system of claim 1 whereinpredetermined data is determined, the predetermined data being relatedto an amount of compression of the spring portion to provide a desirablebonding of the die to the substrate.
 6. The die attach system of claim 5wherein the amount of compression is related to a z-axis position of atleast one of (i) a portion of the bond head, and (ii) a portion of thebond tool.
 7. The die attach system of claim 1 wherein predetermineddata is determined, the predetermined data being related to an amount ofbond force to be applied to provide a desirable bonding of the die tothe substrate.
 8. The die attach system of claim 7 wherein the amount ofbond force is related to a z-axis position of at least one of (i) aportion of the bond head, and (ii) a portion of the bond tool.
 9. Thedie attach system of claim 1 wherein the bond tool includes at least onepin for contacting the die in connection with the transfer from the diesupply source to the substrate.
 10. The die attach system of claim 1wherein the bond tool includes a plurality of pins for contacting thedie in connection with the transfer from the die supply source to thesubstrate.
 11. The die attach system of claim 1 wherein the die supplysource includes an LED wafer, and the plurality of die are a pluralityof LED die.
 12. The die attach system of claim 1 wherein at least one of(i) the die, and (ii) a bonding location of the substrate configured toreceive the die, includes adhesive for securing the die to the bondinglocation after the transfer from the die supply source to the substrate.13. The die attach system of claim 1 wherein the die supply source isconfigured to be positioned between the substrate and the bond toolduring a bonding operation.
 14. A method of attaching a die to asubstrate, the method comprising the steps of: providing a die supplysource including a plurality of die for attaching to the substrate, thedie supply source being positioned between a bond tool and a supportstructure supporting the substrate; and moving the bond tool, carried bya bond head, downward such that a contact portion of the bond toolcontacts the die to transfer the die from the die supply source to thesubstrate, the bond head including a spring portion engaged with thebond tool such that the spring portion is configured to compress duringpressing of the die against the substrate using the contact portion ofthe bond tool.
 15. The method of claim 14 wherein the spring portioncompresses during contact between the contact portion and the die inconnection with the transfer of the die to the substrate using thecontact portion of the bond tool.
 16. The method of claim 14 furthercomprising the step of detecting an amount of compression of the springportion during bonding of the die to the substrate using a sensor. 17.The method of claim 16 further comprising the step of controllingdescent of the bond tool during the moving step based on feedback fromthe sensor.